TWI544496B - Lead-free conductive composition for solar cell electrodes - Google Patents

Description

Lead-free conductive composition for solar cell electrodes Field of invention

The present invention relates to a conductive composition suitable for use in a solar cell electrode formed by a firing penetration method.

Background of the invention

For example, a general lanthanide solar cell has a structure in which an anti-reflection film and a light-receiving surface electrode are provided on a ruthenium substrate belonging to a p-type polycrystalline semiconductor through an n ⁺ layer while being transmitted through a p ⁺ layer. It has a back electrode (hereinafter, it is called "electrode" only when it is not distinguished.). The anti-reflection film is formed of a film of tantalum nitride, titanium oxide, cerium oxide or the like for maintaining sufficient visible light transmittance and reducing surface reflectance.

The light-receiving surface electrode of the solar cell is formed, for example, by a method called baking. In the electrode forming method, for example, after the anti-reflection film is provided on the n ⁺ layer in an entire manner, the conductive paste is applied to the anti-reflection film in an appropriate shape by using, for example, a screen printing method, and is performed. Roasting treatment. According to this method, the electrode is formed in the removed portion as compared with the partial removal of the antireflection film, and the step is simplified, and the problem of dislocation of the removed portion and the electrode formation position is not caused. The conductive paste is, for example, a silver powder, a glass frit (a flaky or powdery glass cullet which is pulverized if necessary after the glass raw material is melted and quenched), an organic vehicle and an organic solvent as main components, and during the baking process, Since the glass component in the conductive paste etches and breaks the antireflection film, the ohmic contact can be formed by the conductor component in the conductive paste and the n ⁺ layer (see, for example, Patent Document 1).

Therefore, in the formation of such a light-receiving surface electrode, it is desirable to improve the ohmic contact, thereby improving the curve factor (FF) or the energy conversion efficiency, and in order to achieve this, various improvements for improving the baking penetration have been tried.

Advanced technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2006-332032

Patent Document 2: JP-A-2008-109016

Patent Document 3: JP-A-2006-313744

Patent Document 4: Special Table 2008-543080

However, lead-free glass without lead has been used in various fields due to concerns about environmental problems, etc. However, lead glass is still used in the aforementioned applications. In this case, when lead-free glass is used in the conductive paste for forming the light-receiving surface electrode by the firing penetration method, the baking temperature is increased as compared with the case where the lead glass is used, and sufficient ohmic contact cannot be obtained. Poor characteristics. Various types of firing temperatures or baking penetrations when using lead-free glass have been disclosed so far. However, those having sufficient characteristics have not yet been obtained.

For example, a conductive composition is disclosed which uses a lead-free glass frit composed of Bi-based glass containing Bi ₂ O ₃ , B ₂ O ₃ , and SiO ₂ as a main component, and is added by adding An additive containing Zn such as ZnO improves electrical properties (see Patent Document 1 above). In the conductive composition, the additive amount of the Zn-containing additive is preferably in the range of 10 (wt%) with respect to the entire composition, and the average particle diameter thereof is preferably less than 0.1 (μm). In the case of the adhesion of the electrode, etc., the amount of the additive containing Zn is preferably small, and in order to obtain an effect in a small amount, it is preferable to use a fine one. However, a small amount and a fine additive are poor in dispersibility and difficult to handle.

Further, there is disclosed a silver paste for a solar cell element which uses ZnO from 5 (wt%) to 10 (wt%), Bi ₂ O ₃ from 70 (wt%) to 84 (wt%), B ₂ The glass frit in which O ₃ + SiO ₂ is 6 (wt% or more) (refer to the aforementioned Patent Document 2). This silver paste is intended to improve the adhesion strength to the substrate and long-term reliability. However, even if a glass frit having a main component within the range of the above composition is used, the bonding strength is not necessarily obtained, and sufficient electrical characteristics cannot be obtained.

Moreover, in the use of lead-free glass for solar cell electrode applications, a thick film conductive composition is disclosed which contains: Al, Cu, Au, Ag, Pd, Pt or any of these alloys or Metal particles of the mixture; lead-free glass; and organic medium (refer to the aforementioned Patent Document 3). The aforementioned lead-free glass system exhibits a composition having a SiO _{2 content} of 0.5 (wt%) to 35 (wt%) and a B ₂ O ₃ of 1 (wt%) to 15 (wt%) in a ratio within the following range. And Bi ₂ O ₃ is from 55 (wt%) to 90 (wt%), ZnO is from 0 (wt%) to 15 (wt%), and Al ₂ O ₃ is from 0 (wt%) to 5 (wt%). When the inner electrode is formed by Al, the soldering of the wire may not be performed. On the other hand, if the bus bar is formed by Ag or Ag/Al, the electric field inside is damaged, and therefore, it is revealed that the formation does not occur. The conductive composition of the electrode of the above-mentioned problem, however, for the purpose of improving the inner electrode, the baking penetration property or the electrical property at the time of receiving the light-receiving electrode is not considered, and if it is the above composition, for example, the softening point Too high a problem.

Further, there is disclosed a light-receiving surface electrode comprising a conductive metal component 85 (wt%) to 99 (wt%), a glass component 1 (wt%) to 15 (wt%), and the glass component contains: Bi ₂ O ₃ is 5 (mol%) to 85 (mol%), and SiO ₂ is 1 (mol%) to 70 (mol%) (refer to Patent Document 4 mentioned above). The light-receiving surface electrode is preferably used for obtaining a sufficient ohmic contact at a low baking temperature even when a lead-free glass is used, and the glass component preferably contains V ₂ O ₅ of 0.1 (mol%) in a ratio within the following range. The oxide of trivalent to 30 (mol%), Al, B, etc. is 1 (mol%) to 20 (mol%), and the tetravalent oxide of Ti, Zr, Hf is 1 (mol%) to 15 (mol%), P, Ta, Nb, Sb, the pentavalent oxide is 0.1 (mol%) to 20 (mol%), the alkali metal oxide is 0.1 (mol%) to 25 (mol%), alkaline earth oxide is 0.1 (mol%) to 20 (mol%), ZnO was 0.1 (mol%) to _{25 (mol%), Ag 2} O to 0.1 (mol%) to 12 (mol%). However, the glass composition described above is broadly applicable as in the scope of the patent application, and no suitable composition is specified for the formation of the light-receiving electrode by baking. On the other hand, although there are several specific glass compositions disclosed in the examples, no matter which glass is used, the electrical characteristics are insufficient, or the softening point is too high to be used in the light-receiving surface electrode.

The present invention has been made in view of the foregoing circumstances, and an object thereof is to provide a lead-free conductive composition for a solar cell electrode which can form an electrode excellent in electrical characteristics.

In order to achieve the above object, the present invention is directed to a lead-free conductive composition for a solar cell electrode, which comprises a conductive powder, a glass frit and a carrier, and (a) the glass frit is composed of a relative glass composition. In terms of oxide, the content of Bi ₂ O ₃ is from 10 (mol%) to 29 (mol%), ZnO is from 15 (mol%) to 30 (mol%), and SiO ₂ is 0 (mol). %) to 20 (mol%), B ₂ O ₃ is 20 (mol%) to 33 (mol%), and the total amount of Li ₂ O, Na ₂ O, and K ₂ O is 8 (mol%) to 21 (mol) %) of at least one lead-free glass.

According to this configuration, the lead-free conductive composition for the solar cell electrode is composed of the lead-free glass having the above-described composition because the glass frit constituting the solar cell electrode is formed, and therefore, if it is used to form the electrode of the solar cell, it is lead-free. However, an electrode having excellent electrical characteristics can be obtained.

Further, in the above glass frit composition, B ₂ O ₃ forms an oxide of glass (i.e., a component of a glass skeleton) and is a component necessary for lowering the softening point of the glass. If it is less than 20 (mol%), the softening point will constitute an excessively high value, and if it is more than 33 (mol%), the electrical characteristics of the solar cell will become insufficient. The less B ₂ O _{3 , the} more the softening point will rise. On the other hand, the more B ₂ O _{3 , the} lower the electrical properties (for example, in the lanthanide solar cell, the cause is generally considered to be related to the substrate material. The reactivity of Si is improved. Therefore, the ratio thereof should be determined in consideration of the desired softening point and electrical characteristics. For example, it is preferably 30 (mol%) or less.

Further, Bi ₂ O ₃ is a component which lowers the softening point of the glass and is required for the low-temperature baking. If it is less than 10 (mol%), the softening point will constitute an excessively high value, and if it is more than 29 (mol%), the electrical characteristics of the solar cell will become insufficient. In order to obtain as high an electrical property as possible, the amount of Bi ₂ O ₃ is preferably less, and more desirably stays below 20 (mol%). Further, in order to sufficiently lower the softening point, the amount of Bi ₂ O ₃ is preferably a large amount, and is preferably 15 (mol%) or more. That is, a range of 15 (mol%) to 20 (mol%) is particularly desirable.

Further, the ZnO-based component which lowers the softening point of the glass and improves the durability (that is, the long-term reliability) is less than 15 (mol%), and the softening point is excessively high, and the durability is also insufficient. On the other hand, if it is more than 30 (mol%), the balance with other components may be affected, but the glass may be easily crystallized. The smaller the amount of ZnO, the higher the softening point and the lower the durability. On the other hand, the more the amount of ZnO, the easier it is to crystallize. Therefore, it is more preferably 20 (mol%) or more. It is desirable to be 30 (mol%) or less. That is, a range of from 20 (mol%) to 30 (mol%) is particularly desirable.

The alkali metal component Li ₂ O, Na ₂ O, and K ₂ O are components which lower the softening point of the glass. When the total amount is less than 8 (mol%), the softening point is excessively high, and if it is more than 21 (mol%) ), the electrical characteristics of the solar cell will become insufficient. The smaller the amount of the alkali metal component, the higher the softening point. On the other hand, the larger the amount of the alkali metal component, the lower the electrical properties. Therefore, it is more preferably 10 (mol%) or more, and more preferably 20 (mol%) or less. That is, a range of 10 (mol%) to 20 (mol%) is particularly desirable.

Further, SiO ₂ forms an oxide of glass and has an effect of improving the stability of the glass. Therefore, although it is not an essential component, it is preferable to contain SiO ₂ . However, the more SiO _{2 , the} higher the softening point and therefore must stay below 20 (mol%). In order to obtain sufficient stability, it is more preferably 4 (mol%) or more, and more preferably 11 (mol%) or less in order to keep the softening point at a sufficiently low value. That is, 4 (mol%) to 11 (mol%) is particularly desirable.

Further, it is not necessarily difficult to specify the form in which each component is contained in the glass. However, the ratios are all converted to oxide values.

Further, the glass constituting the conductive composition of the present invention may contain various other glass constituents or additives in a range that does not impair the properties thereof, and may contain, for example, Al ₂ O ₃ , P ₂ O ₅ , or alkaline earth. Oxides, other compounds. When such a large amount is contained, the electrical characteristics of the solar cell are impaired. Therefore, for example, it may be contained in a total of 20 (mol%) or less.

Here, it is preferable that the glass frit-based average particle diameter of the lead-free conductive composition for a solar cell electrode is 3.0 (μm) or less. According to this, the following conductive composition can be obtained, that is, the printability is further improved, and a higher FF value can be obtained. In addition, when the average particle diameter is 0.5 (μm) or more, the dispersibility at the time of paste adjustment is further improved, so that productivity can be improved.

Further, it is preferable that the lead-free conductive composition for the solar cell electrode contains the glass frit in a ratio ranging from 2 (wt%) to 6 (wt%) with respect to the entire paste. The larger the amount of glass frit, the more the solubility of the reflective film is prevented from increasing and the baking penetration is improved. However, conversely, the larger the amount of frit, the higher the resistance value and the lower the output of the solar cell. Therefore, in order to obtain a sufficiently high baking penetration property, it is preferable to make 2 (wt%) or more, and on the other hand, in order to obtain a sufficiently high solar cell output, it is preferable to stay below 6 (wt%).

Further, it is preferable that the conductive powder is a silver powder. Copper powder, nickel powder, or the like may be used as the conductive powder. However, since silver powder can achieve high conductivity, it is most preferable.

Further, it is preferable that the lead-free conductive composition for the solar cell electrode contains 64 parts by weight to 90 parts by weight of the silver powder and 5 parts by weight to 20 parts by weight of the carrier, in a ratio within the following range. According to this, the following conductive composition can be obtained, that is, the printed property is good and the conductivity is high, and an electrode having good solder wetting can be produced. If the amount of the silver powder is too small, high conductivity cannot be obtained, and if it is too large, the fluidity is lowered and the printability is deteriorated. Further, if the amount of the glass frit is too small, the adhesion to the substrate is insufficient, and if it is too large, the glass will appear on the surface of the electrode after baking and the solder wettability will be deteriorated.

Further, the silver powder is not particularly limited, and the basic effects of the present invention in which the optimum baking temperature range is expanded can be enjoyed when a powder of any shape such as a spherical shape or a scaly shape is used. However, in the case of using a spheroid, for example, since the printing property is excellent and the filling rate of the silver powder in the coating film is improved, it is complementary to the use of silver having high conductivity, compared to the use of scales. When the silver powder of other shapes is used, the conductivity of the electrode formed from the coating film is improved, so that the line width can be made finer while the necessary conductivity is ensured. Therefore, when the conductive composition is applied to the light-receiving surface electrode and the line width is made thinner, the light-receiving area capable of absorbing solar energy can be further increased, so that a solar cell having higher conversion efficiency can be obtained.

In addition, since the conductive composition of the present invention can appropriately control the silver diffusion during the formation of the electrode which is fired and penetrated as described above, it is suitably used for the light-receiving surface electrode. However, it is not limited to the light-receiving surface electrode, and may be used as the inside. electrode. For example, although the inner electrode is composed of an aluminum film covering a full surface and a strip-shaped electrode overlapping the same, it is also preferable to form a constituent material of the strip electrode.

Further, the glass frit may be synthesized from various vitrifiable raw materials according to the above composition range, and examples thereof include oxides, carbonates, nitrates, and the like. For example, cerium oxide may be used as the Bi source. Zinc oxide was used as the Zn source, cerium oxide was used as the Si source, boric acid was used as the B source, lithium carbonate was used as the Li source, sodium carbonate was used as the Na source, and potassium carbonate was used as the K source.

Further, in addition to the main components Bi, Zn, Si, B, and an alkali metal, when a composition containing other components such as Al, P, an alkaline earth metal, or another compound is prepared, for example, oxides and hydrogens may be used. Oxides, carbonates, nitrates, and the like.

Simple illustration

Fig. 1 is a schematic cross-sectional structural view showing a solar cell in which a paste composition for an electrode according to an embodiment of the present invention is applied to a light-receiving surface electrode.

Fig. 2 is a view showing an example of a light receiving surface electrode pattern of the solar cell of Fig. 1.

Form for implementing the invention

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Further, in the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of the respective portions are not necessarily correctly drawn.

Fig. 1 is a cross-sectional structural view showing a lanthanide solar cell 10 to which a conductive composition according to an embodiment of the present invention has been applied in a mode. In the first embodiment, the solar cell 10 includes, for example, a germanium substrate 12 belonging to a p-type polycrystalline semiconductor; n ⁺ layers 14 and p ⁺ layers 16 respectively formed on the upper and lower surfaces thereof; formed on the n ⁺ layer 14 The anti-reflection film 18 and the light-receiving surface electrode 20; and the back electrode 22 formed on the p ⁺ layer 16.

The n ⁺ layer 14 and the p ⁺ layer 16 are provided by forming a layer body having a high impurity concentration on the upper surface of the ruthenium substrate 12, and the thickness dimension of the high concentration layer, that is, the thickness dimension of the layer 14 and the layer 16 is, for example. It is about 0.5 (μm). The impurity included in the n ⁺ layer 14 is, for example, phosphorus (P) belonging to the n-type dopant, and the impurity included in the p ⁺ layer 16 is, for example, boron (B) belonging to the p-type dopant.

In addition, the anti-reflection film 18 is formed of, for example, a film made of tantalum nitride Si ₃ N ₄ or the like, and is provided at an optical thickness of, for example, about 1/4 of a wavelength of visible light, whereby it is 10 (%) or less. For example, a very low reflectance of about 2 (%).

Further, the light-receiving surface electrode 20 is formed of, for example, a thick film conductor having the same thickness, and as shown in Fig. 2, the light-receiving surface 24 is substantially entirely provided in a planar shape as follows: The comb of the thin line. The thick film guiding system is composed of thick film silver containing Ag of about 88 (wt%) to 99 (wt%) and glass of about 1 (wt%) to 12 (wt%), and the glass is oxidized. The value of the substance conversion includes 10 (mol%) to 29 (mol%) of Bi ₂ O ₃ , 15 (mol%) to 30 (mol%) of ZnO, and 20 (mol) of SiO ₂ according to the ratio within the following range. %) below, B ₂ O ₃ is from 20 (mol%) to 33 (mol%), and alkali metal components (Li ₂ O, Na ₂ O, K ₂ O) are in a total amount of 8 (mol%) to 21 (mol%) Lead-free glass. Further, the thickness of the conductor layer is, for example, in the range of 15 (μm) to 20 (μm), for example, about 17 (μm), and the width dimension of each of the thin line portions is, for example, 80 (μm) to 130 (μm). In the range, for example, about 100 (μm), and having high conductivity.

Further, the back electrode 22 is composed of an electrode which is formed by slightly coating a thick film material having aluminum as a conductor component on the p ⁺ layer 16; and a strip electrode 28; The film is formed by coating the entire electrode 26 in a strip shape and consisting of thick film silver. The strip electrode 28 is provided to be able to solder a lead wire or the like to the back electrode 22.

In the solar cell 10 configured as described above, the light-receiving surface electrode 20 is composed of thick film silver as described above, and the thick film silver is contained in the range of 1 (wt%) to 12 (wt%). The lead-free glass is superior in electrical characteristics to a solar cell using a conventional lead-free glass, and has an advantage of having an FF value of 74% or more as much as the case of using lead glass.

The light-receiving surface electrode 20 as described above is formed by, for example, a known paste-through method using a paste for an electrode composed of a conductor powder, a glass frit, a carrier, and a solvent. Hereinafter, a method for producing a paste for an electrode according to a comparative example will be described, and an example of a method of manufacturing the solar cell 10 including the light-receiving surface electrode will be described.

First, the aforementioned glass frit is produced. Prepare cerium oxide as Bi source, zinc oxide as Zn source, cerium oxide as Si source, boric acid as B source, lithium carbonate as Li source, sodium carbonate as Na source, potassium carbonate as K source, alumina as Al source, NH ₄ H ₂ PO _{4 was} used as a P source, calcium oxide CaO as a Ca source, and BaCO ₃ as a Ba source, and weighed and adjusted to the composition shown in the examples of Table 1. Further, each of the above raw materials may be any of an oxide, a hydroxide, a carbonate or a nitrate, but it is preferred to use a finely pulverized raw material to melt easily. This is put into a crucible, and is made vitrified by melting for 20 minutes to 1 hour depending on the temperature in the range of 900 (° C.) to 1400 (° C.). The obtained glass is pulverized by a suitable pulverizing apparatus such as a ball mill to obtain powders having an average particle diameter of 0.4 (μm), 0.6 (μm), 1.5 (μm), 3.0 (μm), and 4.0 (μm).

Further, the conductive powder is, for example, a commercially available spherical silver powder having an average particle diameter of from 0.5 (μm) to 3 (μm), for example, about 2 (μm). By using such a silver powder having an average particle diameter small enough, the filling rate of the silver powder in the coating film can be increased, and the conductivity of the conductor can be improved. Further, the carrier is prepared by dissolving an organic binder in an organic solvent, for example, butyl carbitol acetate is used as the organic solvent, and ethyl cellulose is used, for example, as the organic binder. The proportion of ethyl cellulose in the carrier is, for example, about 15 (wt%). Further, the solvent to be added to the carrier is, for example, butyl carbitol acetate, that is, it is not limited thereto, and may be the same solvent as the user in the carrier, and the purpose of the solvent is to adjust the paste. Viscosity.

Preparing the foregoing paste raw materials separately, and weighing, for example, 80 parts by weight of the conductor powder; 10 parts by weight of the carrier; other suitable amounts of the solvent, the additive; and the glass frit of 2 (wt%) to 6 (wt%) with respect to the entire paste, Further, after mixing by using a stirrer or the like, the dispersion treatment is carried out by, for example, a three-roll mill, whereby the paste for the electrode can be obtained. Further, Table 1 above summarizes the composition of the glass frit in each of the examples and the comparative examples; the amount of addition (wt%) with respect to the entire paste; and the solar cell 10 when the light-receiving surface electrode 20 is formed using each glass frit. The measurement result of the FF value.

The paste for the electrode is prepared as described above, and on the other hand, on the appropriate substrate, for example, the impurity is diffused or injected by a well-known method such as thermal diffusion or ion implantation to form the aforementioned n ^{+ .} The layer 14 and the p ⁺ layer 16 are used to fabricate the germanium substrate 12. Next, a thin film of tantalum nitride (SiN _x ) is formed thereon by a suitable method such as spin coating, and the anti-reflection film 18 is provided.

Next, the paste for the electrode is screen-printed on the anti-reflection film 18 by the pattern shown in Fig. 2 described above. It is dried by, for example, 150 (° C.), and then calcined in a near-infrared furnace at a temperature ranging from 650 (° C.) to 900 (° C.), whereby the paste for the electrode is used in the baking process. The glass component in the middle will prevent the reflection film 18 from being dissolved, and the paste for the electrode will prevent the reflection film 18 from being broken, and therefore, the conductor component in the paste for the electrode, that is, the silver and n ⁺ layer 14 can be obtained. Electrical connection is made, and as shown in FIG. 1 described above, ohmic contact between the germanium substrate 12 and the light-receiving surface electrode 20 can be obtained. The light-receiving electrode 20 is formed in this manner.

Further, the back electrode 22 may be formed after the above-described steps, or may be formed by firing simultaneously with the light-receiving surface electrode 20. When the inside electrode 22 is formed, for example, an aluminum paste is applied to the inside of the ruthenium substrate 12 by a screen printing method or the like, and a total thickness of the entire surface electrode 26 made of a thick aluminum film is formed by performing a baking treatment. In addition, the strip electrode 28 is formed by applying the paste for the electrode to a strip shape on the surface of the entire electrode 26 by a screen printing method or the like and performing a baking treatment. Thereby, the back electrode 22 composed of the entire electrode 26 covering the entire inside and the strip electrode 28 provided in a strip shape on one surface thereof is formed, and the solar cell 10 is obtained. In the above step, when it is produced by simultaneous firing, the printing process is performed before the baking of the light-receiving surface electrode 20.

The FF value shown in the second column from the right in the above-mentioned Table 1 is based on the solar cell 10 obtained in the above, and the examples and comparative examples in which the composition and the amount of the glass have been variously changed are considered as The most suitable calcination temperature is calcined to form the light-receiving surface electrode 20, and the obtained output of the solar cell 10 is measured and found. In addition, the output of the solar cell 10 was measured using a commercially available solar simulator. Further, the "FF value after the moisture resistance test" shown in the right end column is an accelerated test which is maintained at a temperature of 85 (° C.) and a humidity of 85 (%) for 1000 hours under high temperature and high humidity, and the FF value after the test is performed. When the rate of change is 5 (%), the moisture resistance ("○" evaluation) is made, and the value of more than 5 (%) is not moisture resistance ("×" evaluation).

In the solar cell, if the F.F. value of 74 (%) or more can be obtained, it can be used. However, the higher the F.F. value, the more desirable it is. In each of Examples 1 to 11 of Table 1, F.F. values of 75 (%) or more were obtained, and it was confirmed that the characteristics were as high as those in the case of using lead glass.

That is, according to the evaluation results shown in Table 1, if Bi ₂ O ₃ is 10 (mol%) to 29 (mol%), B ₂ O ₃ is 20 (mol%) to 33 (mol%), and SiO ₂ is 20 (mol%) or less, ZnO is 15 (mol%) to 30 (mol%), and an alkali metal component (total of Li ₂ O, Na ₂ O, and K ₂ O) is 8 (mol%) to 21 (mol%) When the total content of other components (Al ₂ O ₃ , CaO, BaO, and P ₂ O ₅ ) is 18 (mol%) or less, the FF value can be sufficiently increased.

Further, according to Example 2, Example 5, and Example 7, if Bi ₂ O ₃ is 15 (mol%) to 20 (mol%), B ₂ O ₃ is 26 (mol%) to 30 (mol%), SiO ₂ is 4 (mol%) to 17 (mol%), ZnO is 28.5 (mol%) to 30 (mol%), and the alkali metal component (total of Li ₂ O, Na ₂ O, K ₂ O) is 17 ( When the total amount of mol%) to 21 (mol%) and other components (Al ₂ O ₃ , CaO, BaO, P ₂ O ₅ ) is 3 (mol%) or less, an FF value of 77.0 (%) can be obtained. .

Further, in any of the first to eleventh examples, the change in the F.F. value after the moisture resistance test was kept within 5 (%), and it was confirmed that the long-term reliability was sufficient.

On the other hand, in Comparative Example 1 to Comparative Example 10, the FF value stayed at less than 70 (%). In Comparative Example 1, Comparative Example 3, and Comparative Example 7, it is considered that since Bi ₂ O _{3 is} too large, electrical characteristics are lowered, and since the amount of ZnO is too small and the amount of the alkali metal component is too small or zero, the softening point is too high. , the FF value will decrease. Further, in Comparative Example 2 and Comparative Example 6, it is considered that since Bi ₂ O _{3 is} too large, electrical characteristics are lowered, and since B ₂ O _{3 is} too small, the softening point is too high, so that the FF value is lowered. Further, in Comparative Example 4, it is considered that since Bi ₂ O ₃ and B ₂ O _{3 are} excessive, electrical characteristics are lowered and the FF value is lowered. It is generally believed that excessive boron is affected by the reaction of the ruthenium belonging to the substrate material. Further, in Comparative Example 5, it is considered that since Bi ₂ O _{3 is} excessive, electrical characteristics are lowered and the FF value is lowered. Further, in Comparative Example 8, it is considered that since Bi ₂ O _{3 is} too small and SiO _{2 is} too large, the softening point is too high, and since B ₂ O _{3 is} too large, electrical characteristics are lowered, so that the FF value is lowered. Further, in Comparative Example 9, it is considered that since the amount of ZnO is too large, the glass crystallizes, so that the FF value is lowered. Further, in Comparative Example 10, it is considered that since B ₂ O _{3 is} too large, electrical characteristics are lowered, and since ZnO is excessively large, the glass is easily crystallized, and since the alkali metal component is not contained, the softening point becomes too high. Therefore, the FF value will decrease.

Further, in Comparative Example 1 to Comparative Example 10, although Comparative Example 11 to Comparative Example 13 were able to obtain a high FF value, they stayed at 70 (%) to 72 (%). In Comparative Example 11, it is considered that since B ₂ O _{3 is} too small, the softening point is increased, and since ZnO is excessively large, the glass is easily crystallized, so that the FF value is lowered as compared with the examples. Further, in Comparative Example 12 and Comparative Example 13, it is generally considered that there is no problem in the glass component ratio. However, since the amount of glass added when preparing the paste for the electrode is too small, sufficient baking penetration cannot be obtained, and it is impossible to obtain sufficient baking performance. A good ohmic contact is obtained, or the amount of glass added is too large, so that the resistance value of the electrode material becomes too high, so the FF value stays at a lower value. Further, in Comparative Example 14, a sufficiently high FF value was obtained, however, the change after the moisture resistance test was more than 5 (%), and the long-term reliability was insufficient. It is considered that since the amount of Si is too large, the softening point is increased and the moisture resistance is insufficient.

Further, Examples 8 to 11 used a glass frit of the same composition to change the amount of addition relative to the entire paste between 2 (wt%) and 6 (wt%), and evaluated the F.F. value of the solar cell 10. As shown in the evaluation results, if the addition amount is in the range of 2 (wt%) to 6 (wt%), the change in the FF value cannot be seen irrespective of the addition amount, however, as in the above Comparative Example 12 and Comparative Example 13, As shown, if the addition amount constitutes 1 (wt%) and 7 (wt%), the FF value is slightly lowered. Therefore, in order to obtain a sufficiently high F.F. value, the glass addition amount is preferably in the range of 2 (wt%) to 6 (wt%).

As described above, the paste for the solar cell electrode of the present embodiment is composed of a lead-free glass having a composition within the following range, that is, Bi ₂ O ₃ is 10 (mol%) to 29 (mol%), B ₂ O ₃ is 20 (mol%) to 33 (mol%), SiO ₂ is 20 (mol%) or less, ZnO is 15 (mol%) to 30 (mol%), alkali metal component ( The total of Li ₂ O, Na ₂ O, and K ₂ O is 8 (mol%) to 21 (mol%), and the total of other components (Al ₂ O ₃ , CaO, BaO, P ₂ O ₅ ) is 18 (mol). In the case of forming the light-receiving surface electrode 20 of the solar cell 10, it is not lead-free, but has an advantage that the FF value is 75 (%) or more and an electrode having excellent electrical characteristics can be obtained. .

Further, according to the paste for an electrode of the present embodiment, since the amount of ZnO is in the range of 15 (mol%) to 30 (mol%), the long-term reliability is also excellent, and also has the following advantages: The rate of change of the FF value after the 1000-hour high-temperature and high-humidity test is only 5 (%) or less.

Further, in the present embodiment, in particular, when the amount of glass in the electrode paste is 2 (wt%) to 6 (wt%), there is almost no difference in characteristics due to the amount of glass, and it is enjoyable. According to the advantages of the high electrical properties of its glass composition.

The present invention has been described in detail above with reference to the drawings. However, the present invention may be embodied in other embodiments without departing from the spirit and scope of the invention.

For example, in the foregoing embodiment, the anti-reflection film 18 is composed of a tantalum nitride film, however, the constituent material thereof is not particularly limited, and titanium dioxide TiO ₂ generally used in solar cells can be used similarly. And other various materials.

Further, in the embodiment, the present invention is applied to the case of the lanthanide solar cell 10. However, in the present invention, as long as the solar cell can form the light-receiving surface electrode by the firing penetration method, the substrate material to be applied is not Special restrictions.

10. . . Solar battery

12. . .矽 substrate

14. . . n ⁺ layer

16. . . p ⁺ layer

18. . . Anti-reflection film

20. . . Light-receiving electrode

twenty two. . . Inside electrode

twenty four. . . Light receiving surface

26. . . Full electrode

28. . . Strip electrode

Fig. 1 is a schematic cross-sectional structural view showing a solar cell in which a paste composition for an electrode according to an embodiment of the present invention is applied to a light-receiving surface electrode.

Fig. 2 is a view showing an example of a light receiving surface electrode pattern of the solar cell of Fig. 1.

10. . . Solar battery

12. . .矽 substrate

14. . . n ⁺ layer

16. . . p ⁺ layer

18. . . Anti-reflection film

20. . . Light-receiving electrode

twenty two. . . Inside electrode

twenty four. . . Light receiving surface

26. . . Full electrode

28. . . Strip electrode

Claims (8)

A lead-free conductive composition for a solar cell electrode, comprising a conductive powder, a glass frit and a carrier for a lead-free conductive composition for a solar cell electrode, wherein the frit is composed of at least one of the following lead-free glasses; In the lead conversion, the lead-free glass is contained in a ratio of the range of the following to the entire glass composition in the range of 15 to 20 (mol%) of Bi ₂ O _{3 and} 28.5 to 30 (mol%) of ZnO. SiO ₂ is 4 to 17 (mol%), B ₂ O ₃ is 26 to 30 (mol%), and the total amount of Li ₂ O, Na ₂ O, and K ₂ O is 17 to 21 (mol%), and other components are The total amount is 3 (mol%). The lead-free conductive composition for a solar cell electrode according to the first aspect of the invention, wherein the lead-free glass further contains another glass component of any one of Al ₂ O ₃ , P ₂ O ₅ and an alkaline earth oxide. Or additives. A lead-free conductive composition for a solar cell electrode according to the first or second aspect of the invention, wherein the glass frit has an average particle diameter of 3.0 (μm) or less. The lead-free conductive composition for a solar cell electrode according to the first or second aspect of the patent application, which contains the glass frit in a ratio of 2 to 6 (wt%) based on the entire composition. A lead-free conductive composition for a solar cell electrode according to claim 1 or 2, wherein the conductive powder is a silver powder. The lead-free conductive composition for solar cell electrodes according to claim 5, which comprises 64 parts by weight to 90 parts by weight of the silver powder and 5 parts by weight of the carrier to the ratio within the following range 20 parts by weight. A lead-free conductive composition for a solar cell electrode according to the fifth aspect of the invention, wherein the silver powder is a powder having a spherical shape or a scaly shape. A lead-free conductive composition for a solar cell electrode according to claim 1 or 2, which is used as a light-receiving surface electrode and/or a back electrode of the solar cell.